1. Field of the Invention
The present invention relates to a platinum complex compound useful as a light emitting material and an organic electroluminescence device (which may hereinafter be called “organic EL device”) using the platinum complex compound.
2. Description of the Related Art
Research and development on organic electroluminescence devices are actively performed in recent years because they provide high-luminance emission at a low driving voltage. In general, organic EL devices have organic layers including a light emitting layer and a pair of electrodes sandwiching the organic layers therebetween. Electrons injected from a cathode and holes injected from an anode recombine in the light emitting layer and energy of excitons thus formed is made use of for light emission.
Use of a phosphorescent material has accelerated improvement in efficiency of devices. As the phosphorescent material, iridium complexes and platinum complexes are known (JP-A-2005-220136).
There is a report on the use of platinum complexes having a tetradentate for obtaining organic EL devices having improved emission efficiency and durability (International Patent Publication No. 04-108857). Of these platinum complexes, complexes having a pyridylpyridine skeleton enable shortening of an emission wavelength compared with complexes having a phenylpyridine skeleton so that they are promising as materials emitting light of from light-blue to blue color. It is however difficult to control generation of complexation byproducts so that establishment of a practical preparation process of them is required.
There is also a report on a blue light emitting material having a pyridylpyrazole skeleton and an organic EL device using it (JP-A-2007-19462), but this development has not succeeded in obtaining a device satisfying both high efficiency and durability particularly when it is used as a high luminance device. In consideration of the applications of organic EL devices to lighting apparatuses, however, use of them as a high luminance device is required. There is accordingly a demand for the development of blue-light emitting materials showing excellent durability even if they are used for such a high luminance device.